Traction mechanism drives of internal combustion engines conventionally have a crankshaft drive input gear wheel, at least one camshaft drive output, gear wheel and a chain or a toothed belt as a wrap-around means. They are subject, on account of torque fluctuations or angular speed changes, to oscillation excitations which lead to increased frictional forces and can adversely affect the service life and efficiency of the wrap-around means.
A system for active damping of vibrations is known from DE 44 23 577 A1, in which system an electric machine is used to reduce rotational non-uniformities. The electric machine comprises a flywheel which can be attached to the crankshaft of an internal combustion engine and has a stator, which interacts with said flywheel, as a fixed machine part which has excitation coils, so that the shaft can be braked or accelerated. In this way, influence can be exerted on the rotation of the shaft in a targeted manner in order to reduce non-uniformities such as speed fluctuations.
It is proposed in DE 40 15 701 A1 to influence rotational speed fluctuations, which occur during operation of a reciprocating piston internal combustion engine, by means of an electric machine which is connected to an energy source, for example the vehicle battery.
Said concepts have, however, not yet found their way into series production since extremely high electric currents of up to 200 A flow when damping rotational non-uniformities, so that an expensive cooling system is required.
With regard to optimizing their efficiency, traction mechanism drives and specifically camshaft drives of internal combustion engines are increasingly designed in a friction-reduced fashion, for example by using roller cam followers. This results, however, in the resetting torques of the camshafts increasing disproportionately, resulting in pronounced rotational non-uniformities of the shafts. The driven camshafts therefore disadvantageously influence the dynamic behavior of the traction mechanism drive. Engine elements which are connected to the camshaft, such as gasoline pumps, vacuum pumps, control drives etc., are afflicted by said increased dynamic loading, so that high expense is required in order that said components reach the demanded service life.